Patna: BJP stuck to its demand for Prime Minister Manmohan Singh's resignation on the 'coalgate' scam and said it would not let Parliament function till he demits office owning up responsibility.

"There is no (no) question of the opposition letting off pressure on the Prime Minister to quit his office as he has been squarely responsible for the Rs 1.86 lakh crore coal scam which has taken place right under his nose as he held the coal portfolio for five years between 2005-09 in UPA I government," BJP national spokesman Ravishankar Prasad said.

"The Prime Minister's resignation was all the more warranted to give CBI - probing the irregularities in coal blocks allotment - a free hand to carry out the investigation as the agency directly functions under his command," he said.

The CBI will not be able to freely discharge its duties so long as Singh remained in office as the agency will also probe his role in the capacity as the coal minister, Prasad said.

Prasad said that it was for the first time Singh has been implicated in a scam as he headed the coal ministry during which the allotment of 145 coal blocks took place.

He also tore into Union Finance Minister P Chidambaram's defence of the UPA government and the Prime Minister on the coal scam and said that the latter had committed a mistake similar to his colleague Kapil Sibal in the 2G scam that later turned out to be false.